1. Field of the Invention
The present invention relates generally to stimulating medical devices and, more particularly, to combined optical and electrical neural stimulation.
2. Related Art
Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, a person may have hearing loss of both types. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss is often addressed with conventional hearing aids which amplify sound so that acoustic information can reach the cochlea.
In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. Sensorineural hearing loss occurs when there is damage to the inner ear or to the nerve pathways from the inner ear to the brain. Those suffering from sensorineural hearing loss are thus unable to derive suitable benefit from conventional hearing aids. As a result, specific neural-stimulating devices, referred to herein as electrically-stimulating auditory prostheses, have been developed to provide persons having sensorineural hearing loss with the ability to perceive sound. Such electrically-stimulating auditory prostheses deliver electrical stimulation to nerve cells of the recipient's auditory system.
As used herein, the recipient's auditory system includes all sensory system components used to perceive a sound signal, such as hearing sensation receptors, neural pathways, including the auditory nerve and spiral ganglion, and parts of the brain used to sense sounds. Electrically-stimulating auditory prostheses include, for example, auditory brain stimulators and Cochlear™ prostheses (commonly referred to as Cochlear™ prosthetic devices, Cochlear™ implants, Cochlear™ devices, and the like; simply “cochlear implants” herein.)
Most sensorineural hearing loss is due to the absence or destruction of the cochlear hair cells which transduce acoustic signals into nerve impulses. It is for this purpose that cochlear implants have been developed. Cochlear implants use direct electrical stimulation of auditory nerve cells to bypass absent or defective hair cells that normally transduce acoustic vibrations into neural activity. Such devices generally use an electrode array implanted into the scala tympani of the cochlea so that the electrodes may differentially activate auditory neurons that normally encode differential pitches of sound.
Auditory brain stimulators are used to treat a smaller number of recipients with, for example, bilateral degeneration of the auditory nerve. For such recipients, the auditory brain stimulator provides stimulation of the cochlear nucleus in the brainstem.